Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT01586 (G418)
 2,237 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The fourth cytoplasmic domain, the so-called C-terminal juxtamembrane segment or helix VIII, has been identified in numerous G-protein-coupled receptors and exhibits unique functional characteristics. Efforts have been devoted to studying the juxtamembrane segment in order to understand the biological importance of the segment in G-protein activation of the cannabinoid CB1 and CB2 receptors. Recent biochemical data revealed that the CB1 C-terminal juxtamembrane peptide fragment CB1-(401-417) can directly activate the G-protein and also showed that the specificity of the signal transduction activation by the C-terminal juxtamembrane region is unique to the CB1 receptor but not to the CB2 receptor (Mukhopadhyay, S., and Howlett, A. C. (2001) Eur. J. Biochem. 268, 499-505). However, there is experimental work, not yet reported, on the conformational analyses and structural comparison between the respective helix VIII segments of the two receptors. In the present study, we have examined the conformational specificities of the cytoplasmic helical domains for both cannabinoid receptors. Three-dimensional structural features of two synthetic CB1 and CB2 peptides, CB1I397-G418 and CB2I298-K319, respectively, in membrane mimetic DPC micelles were studied using a combined high resolution NMR and computer modeling approach. Comparisons of the NMR-determined structures of the two peptides as well as their correspondent mutant peptides revealed their conformational properties and salt bridge dissimilarity, which might help us to understand the different structural roles of the fourth cytoplasmic helices in the function and regulation of CB1 and CB2 receptors.
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PMID:NMR structural comparison of the cytoplasmic juxtamembrane domains of G-protein-coupled CB1 and CB2 receptors in membrane mimetic dodecylphosphocholine micelles. 1555 Mar 82

The human thromboxane A(2) (TXA(2)) receptor (TP) is known to mediate platelet aggregation and vasoconstriction. The receptor predominantly interacts with the Gq protein, thereby activating phospholipase C and increasing the intracellular calcium level. In this study, we synthesized a 15-residue peptide corresponding to the C-terminal domain of the Gq protein alpha subunit (Galphaq-Ct peptide) and characterized its interaction with recombinant TP purified from a baculovirus expression system in the presence and absence of an agonist using fluorescence and NMR spectroscopic studies. With fluorescence binding assays, we demonstrated that the Galphaq-Ct peptide was bound to TP, in the absence of the agonist, with a K(d) value of approximately 17 muM. Interestingly, upon addition of the agonist, U46619, the Galphaq-Ct peptide's binding affinity for this activated TP was reduced, thereby increasing the K(d) value to approximately 240 muM. NMR experiments demonstrated that the TP-bound Galphaq-Ct peptide shows a different affinity and conformation, in the absence and presence of the agonist, U46619. This suggested there is the possibility of ligand-free constitutive TP signaling through Galpha binding. Thus, an HEK293 cell line that stably expresses human TP and lacks the ability to produce TXA(2) was created by gene transfer and G418 selection. In comparison with the control cells, the stable cell line showed significant Galpha-mediated ligand-free calcium signaling. The study indicates a promising new outlook for the examination of prostanoid receptor-G-protein interactions in greater detail using integrated NMR spectroscopy, the purified receptor, and the stable cell line.
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PMID:Structural and functional analysis of the C-terminus of Galphaq in complex with the human thromboxane A2 receptor provides evidence of constitutive activity. 2059 Jan 59